The present disclosure relates generally to exhaust gas-driven turbochargers having a waste gate for bypassing exhaust gas around the turbine during certain operating conditions. The disclosure relates in particular to an electro-pneumatic actuator for effecting movement of the waste gate.
Recent increases in gasoline turbocharger performance requirements and stricter emission regulations have driven the need for waste gate actuation to move from pneumatic systems to electric systems for increased controllability, faster response time, and potentially reduced overall system costs. The difficulties associated with electric actuation are, among others, the need to over-size the electric motor because the motor is required to operate in a stall condition for extended periods of time in order to maintain the waste gate in a closed position against high loads. Typically in a continuous stall condition, an electric motor, because of internal heating of the motor coils, can provide less than half of its peak force. This means that there must be a significant over-sizing of the motor to ensure it has sufficient force in the stall condition, which results in large package size, increased weight, and unnecessary force surplus during more-favorable operating conditions.